1. Field of the Invention
The present invention relates to a semiconductor device having a circuit which includes thin film transistors (hereinbelow, abbreviated to “TFTs”), and a method of manufacturing the semiconductor device. More particularly, it relates to, for example, an electro-optical device which is represented by a liquid-crystal display panel, and an electronic equipment on which such an electro-optical device is installed as a component.
Incidentally, here in the specification, the expression “semiconductor device” is intended to signify general devices which function by utilizing semiconductor properties, and it shall cover all of electro-optical devices, semiconductor circuits and electronic equipment.
2. Description of the Related Art
Thin film transistors (hereinbelow, abbreviated to “TFTs”) can be formed on a transparent substrate, and the developments of their applications to an active matrix type liquid-crystal display (hereinbelow, termed “AM-LCD”) have therefore been positively fostered. Since the TFTs utilizing a crystalline semiconductor film (typically, a crystalline silicon film) can attain a high mobility, it is permitted to present an image display of high definition by integrating functional circuits on an identical substrate.
In recent years, note has been taken of technology which constructs TFTs by the use of a semiconductor thin film (whose thickness is on the order of several-several hundred nm) formed on a substrate having an insulating surface. The TFTs have been extensively applied to ICs and electron devices such as an electro-optical device, and the development thereof has been expedited especially as the switching elements of an image display device.
Although various applications utilizing such an image display device have been expected, applications to portable equipment have been especially noticed. Attempts have therefore been made to form TFT elements on a plastics film having a flexibility.
Since, however, the heat resistance of the plastics film is low, the highest temperature of a manufacturing process is inevitably set low. As a result, it is the present situation that TFTs of favorable electric characteristics as in the case of forming them on a glass substrate cannot be formed. Therefore, a liquid-crystal display device of high performance employing the plastics film has not been realized yet.
Besides, the AM-LCD is basically constructed so that a pixel unit for displaying an image, a gate driver circuit for driving the TFTs of individual pixels arrayed in the pixel unit, and a source driver circuit (or a data driver circuit) for transferring image signals to the respective TFTs are formed on the identical substrate.
There has recently been proposed a system-on-panel wherein, not only the pixel unit and the driver circuits, but also signal processing circuits such as a signal dividing circuit and a γ correction circuit are disposed on the identical substrate.